The present invention relates to a color sorting machine for cereal grain or the like and, more particularly, to a color sorting machine provided with a dust collecting device.
A conventional sorting machine of this type is adapted to let raw material, such as cereal grains, fall down linearly, subject the raw material to light and sort out particles of different colors, such as deteriorated or broken grains and foreign matters from the raw material in accordance with a difference in reflected light. For this purpose, the sorting machine has a down chute descending toward a front side of the machine for letting the raw material slide or flow down, a photoelectric detection device which comprises light sources, light-receiving elements and backgrounds, and an injection nozzle device. The photoelectric detection device generates an electric signal upon detection of a different-color particle, and in response to this detection signal, the injection nozzle device is operated to sort the different-color particle.
Such a sorting machine can be seen in U.S. Pat. Nos. 4,371,081, 4,940,850, 5,487,472 and 5,638,961, all of which are of the same assignee as the present invention, and in U.S. Pat. Nos. 4,513,868 and 4,699,273.
Also known is a color sorting machine of the type having a dust collecting device in addition to the components described above. Such a sorting machine is disclosed in Japanese Patent Application Laid-Open Nos. Sho 55-159881, 56-10379, 57-65367 and 61-21775, which are all of the same assignee as the present invention, and in Japanese Patent Application Laid-Open No. Hei 3-89980 and.
An example of the color sorting machine provided with the dust collecting machine is shown in FIG. 3. In the sorting machine, an injection nozzle device 400 injects air to raw material so as to sort particles of different colors. At this time, dust is scattered from the raw material and floats in the machine. When the floating dust sticks to light sources 200a, light-receiving elements 200b and transparent plates 200c for covering these components in a photoelectric detection device 200, light emitted from the light sources 200a is attenuated, and therefore, the detection sensitivity of the light-receiving elements 200b becomes low. As a result, the photoelectric detection device 200 causes a wrong operation in its detection, thereby deteriorating the sorting performance.
The dust collecting device 500 continuously sucks the dust in suspension in the machine by means of a fan 500b to prevent the performance of the photoelectric detection device 200 from being deteriorated. The dust collecting device 500 is disposed on the bottom 600a side of a tilted down chute 600. Therefore, cleaning of the dust collecting device 500 is carried out on the rear side of the machine. In the case where the sorting machine is installed with its back against a wall or the like, the machine itself has to be moved to provide a work space for every cleaning of the dust collecting device. Cleaning of such a dust collecting device is thus troublesome.
On the other hand, the injection nozzle device 400 is situated on the open or flow passage side of the down chute 600, that is, with a nozzle 400a directed from the right side of the down chute 600 to a locus a of coming down of the raw material particles in FIG. 3. Meanwhile, the raw material particles frequently slide down the down chute 600 in plural layers. In this case, particles in the first layer flow down linearly along the bottom 600a of the down chute 600. The second and subsequent layers of particles are not guided by the bottom 600a, and there are cases where they deviate toward the open side of the down chute and disturb the flow. When the thus scattering particles are out of the coming-down locus a and hit the nozzle 400a or its vicinity, they are judged as being different-color particles, even if they are whole grains or particles of good quality. Therefore, the injection nozzle device 400 and the coming-down locus a have to be separated at a certain distance from each other, so that the upper layers of particles do not contact the nozzle 400a and its vicinity. On the contrary, if the distance between the injection nozzle device 400 and the coming-down locus a is too large, the flow of injected air is excessively enlarged or expanded. This results in that not only particles to be discharged but also surrounding particles are removed. The sorting precision is thus deteriorated.